.container {
    width: 1000px;
    margin: 0 auto;   /*0 auto 0 auto*/
}
.header {
    height: 50px;
    background: lightgreen;
}
.main {
    height: 300px;
    background: oldlace;
}
.footer {
    height: 50px;
    background: lightgreen;
    text-align: center;
    line-height: 50px;   /*文字行高是50px*/
}
.footer a:link{    /*footer类中的a设置*/
    text-decoration: none;
}
